A conventional photoresist pattern forming process, which is one of semiconductor device fabricating processes, includes the steps of forming a resist film on a surface of a semiconductor wafer (hereinafter, referred to simply as “wafer”) by applying a resist to the surface of the wafer, exposing the resist film in a predetermined pattern, and developing the exposed resist film. Generally, this photoresist pattern forming process is carried out by a system built by connecting an exposure system to a coating and developing system,
Improve of exposure resolution has been desired to cope with the progressive miniaturization of device patterns and the progressive thickness reduction of films. While exposure techniques using EUVL, EUV and F2 light sources have been developed to improve exposure resolution, immersion exposure has been studied to improve resolution through the further improvement of the existing exposure techniques using existing ArF and KrF light sources. There is a strong trend of the semiconductor device industry and the semiconductor device fabricating system industry toward extending the life of the ArF exposure system as long as possible for financial advantages. Some have an opinion that an ArF light source is used when a desired resolution is 45 nm or above and the use of the EUV light source (extreme ultraviolet light source) will be postponed. Immersion exposure exposes an object to light through, for example, a pure water film. Immersion exposure utilizes the characteristic of light that the wavelength of light shortens in water. For example, the wavelength of ArF light shortens from 193 nm in air to about 134 nm in water.
An exposure system that carries out an immersion exposure process will be briefly described with reference to FIG. 16. An exposure device 1 is placed opposite to a surface of a wafer W held in a horizontal position by a wafer holding mechanism, not shown. The exposure device 1 is provided on its head with a lens 10. Light emitted by a light source, not shown, such as an ArF light source or a KrF light source, travels through the lens 10 and a pattern mask and falls on a resist film formed on the surface of the wafer W to form a latent image of a circuit pattern in the resist film. The head of the exposure device 1 is provided with a pouring hole 11, through which a transparent liquid, such as ultrapure water, is poured, and a suction hole 12. Water is poured through the pouring hole 11 onto a surface of a wafer W to form a water film between the lens 10 and the surface of the wafer W. The water wetting the surface of the wafer W is recovered by sucking the water through the suction hole 12. Thus the transparent water film fills up the gap between the lens 10 and the surface of the wafer W. Light traveled through the lens 10 travels through the water film and falls on the resist film to form a latent image of a predetermined pattern. Then, the wafer W coated with the water film is translated to align the next exposure field in the surface of the wafer W with the exposure device 1 and then the next exposure field is exposed. Thus exposure fields in the surface of the wafer W are exposed successively by step-and-repeat exposure.